1. Field of the Invention
The present invention relates to fuel mixtures utilized in hypergolic propulsion systems. More specifically, the invention relates to hypergolic fuel mixtures of tertiary amines and amine azides, or amines and imidic amides.
2. Description of the Related Art
A liquid or gel bipropellant rocket propulsion system consists of gas generators, oxidizer and fuel propellant tanks, plumbing, oxidizer and fuel valves, and an engine. The bipropellant rocket propulsion unit begins operation when the gas generators have been initiated and the gases from the gas generator pressurize oxidizer and fuel propellant tanks. When the oxidizer and fuel valves open, the pressurized oxidizer and fuel tanks then force the propellants through the plumbing into the engine where the propellants are mixed and ignited. The propellants can be ignited by either ignition aids or by hypergolic (spontaneously self-igniting) chemical reaction. Since ignition aids can take up valuable space in the propulsion system, a hypergolic chemical reaction is the preferred ignition method. Inhibited red fuming nitric acid (hereinafter, IRFNA) and monomethyl hydrazine (hereinafter, MMH) have been the preferred hypergolic rocket oxidizer and fuel for rocket propulsion systems for some time, by providing a high specific impulse and density specific impulse, and providing a short ignition delay of approximately 3 milliseconds or less to approximately 15 milliseconds (depending on test techniques), before ignition after combining of an oxidizer and MMH. A short ignition delay characteristic is important since a long ignition delay of approximately 25 millisecond or longer causes fuel and oxidizer to accumulate in the combustion chamber, so that when ignition does take place an overpressurization can occur with creation of a “hard start.” Overpressurization in the combustion chamber can be severe enough to destroy the rocket motor and negate achievement of the mission objective.
A main drawback of MMH is the high toxicity of the compound. Classified as a suspected human carcinogen, MMH requires exceptional safety precautions during handling which makes fueling of rocket motors both time consuming and expensive. A non-carcinogenic alternative to MMH which can be readily utilized in hypergolic bipropellant propulsion systems is preferred.
U.S. Pat. No. 6,013,143, issued to D. M. Thompson and assigned to the Secretary of the Army, discloses liquid or gel bipropellant fuel compounds which are alternatives to use of potentially carcinogenic compound MMH in rocket propulsion systems similar to a system illustrated in U.S. Pat. No. 5,133,183. The hypergolic fuel compounds disclosed in the '143 patent include three tertiary amine azide compounds consisting of 2-N,N-dimethylaminoethylazide (identified as DMAZ), bis(ethyl azide) methylamine (identified as BAZ), and pyrrolidinylethylazide (also identified as 2-(N-pyrrolidinyl)ethylazide, or PYAZ). The '143 patent disclosed that use of MMH as a fuel mixture with IRFNA would deliver a specific impulse of 284 lbf sec/Ibm and a density impulse of 13.36 lbf sec/cubic inch. Under similar operating conditions, DMAZ delivered a specific impulse of 287 lbf sec/Ibm and a density impulse of 13.77 lbf sec/cubic inch. To achieve performance comparable to MMH used in a rocket propulsion system, the '143 patent disclosed each one of the tertiary amine azides (DMAZ, BAZ or PYAZ) were combined with an oxidizer selected from the group of oxidizers consisting of IRFNA, nitrogen tetroxide, hydrogen peroxide, hydroxyl ammonium nitrate, and liquid oxygen. The '143 patent did not disclose alternative oxidizer compounds which may provide similar or improved performance when combined with DMAZ, BAZ or PYAZ. A limitation of the compounds disclosed in the '143 patent included, for each of the three hydrocarbon moieties attached to the tertiary amine, that at least one but no more than two moieties contained an azide group. A further limitation of the '143 patent includes the tertiary amine azide molecule can have no more than seven carbon atoms for the compound to remain hypergolic, allowing the tertiary amine azides to produce adequate specific impulse or density specific impulse results when mixed with IRFNA.
U.S. Pat. No. 6,210,504, issued to D. M. Thompson and assigned to the Secretary of the Army, discloses a gas generator fuel source for a liquid or gel gas generator system, including the three tertiary amine azide compounds disclosed in the '143 patent, specifically DMAZ, BAZ, and PYAZ. The '504 patent discloses that any one of the three tertiary amine azide compounds is contained and heated in an iridium catalytic reactor bed to achieve a self sustaining decomposition reaction to yield gaseous products for pressurization of the liquid or gel gas generator system. The '504 patent does not disclose alternative tertiary amine azide compounds which may provide similar or improved performance when used instead of, or in combination with DMAZ, BAZ or PYAZ. Limitations of the structure and radicals attached to the tertiary amine azide compounds are relevant to the '504 patent as also disclosed in the '143 patent. The '504 patent discloses solid additives and gellant additives consistent with the additives disclosed in the '143 patent, including use of a gallant such as silicon dioxide, clay, carbon, and polymeric gallant.
It is desirable to provide a plurality of hypergolic fuel mixtures exhibiting minimal toxicity, classified as a non-carcinogen, and having a short ignition delay when mixed in a propulsion system. It is also desirable to provide a plurality of fuel mixtures having a short ignition delay and a density specific impulse competitive with MMH fuel. It is further desirable to provide a plurality of hypergolic fuel mixtures containing a tertiary diamine, tertiary tri-amine or a tetra-amine compound, any of which is mixed with an amine azide compound, a monocyclic amidine compound, or a multi-cyclic amidine compound, for use in propulsion systems as replacements for MMH fuel.